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98                                   SODIUM CHLORATE

substance) or with Leblanc soda, 50 c.c. ( = 5 grams) of solution are neu
tralised exactly with N-nitric acid, the liquid boiled, 10 drops of 10% potas-
sium chromate solution added, and N/io-silver nitrate run in from a burette
until a red coloration appears, i c.c. N/io-silver nitrate = 0-005846 gram

(g) SODIUM SULPHATE. With Leblanc soda, 50 c.c. (~ 5 grams of
substance) or with ammonia, soda, loo c.c. (~-~ 1:0 grams) of the solution
are acidified with hydrochloric acid, heated to boiling, precipitated with
barium chloride, filtered and the barium sulphate1 washed, dried, calcined
and weighed: i gram of BaSO, ~; 0-6089 gram of NaaSO4.

(//.) SILICA AND ALUMINA. 100 c.c. of the solution (~:ro grams of
substance) are acidified with hydrochloric acid and evaporated on a water-
bath, the residue being dried at 105" and taken up in hydrochloric acid ;
the silica is separated and weighed, and the alumina estimated in the solution
in the ordinary way.

Commercial soda crystals .should contain a,t least 34% of N<u(X);i ; usually
they contain 35% (theoretically 37-04;!% NaBC !(')., and <>.:-<>58% 1U>). Some-
times a slight excess of water is present, but this should not exceed r% ; often
slight efflorescence is shown. The ordinary impurity is sulphate (in Leblanc
soda ; see later), but large proportions, such as to -'.<)%, must; bo regarded as
added artificially. The chloride content in Leblane soda, should not: exceed
'5%- The yellowish colour of certain soda crystals is usually derived from
organic and not from iron.

Calcined Lt'.hlan c> soda may contain small proportions of hydroxide, sulphide
and sulphite, and is often contaminated with sulphate ; its strength may vary
from 80 to 0.0%, but: is most, often H8 '95%. A HUIWH.M xtxfa, contains chloride,
and sometimes small quantities of bicarbonate ; its strength is 95 -98%.

The moisture of calcined soda is usually 0-5-1%, 3% being tolerated ; in
moist air, calcined soda may absorb up to about; 10% of moisture,

The insoluble substances in ordinary good soda should, not exceed 0-5%, of
which about o-i % is insoluble in. hydrochloric acid and 0-02% ferric, oxide.

The sulphate in ammonia soda, should not be more than 0-1%, if not added.
In Leblanc soda of best quality 0-5 -'i % occurs, while in inferior qualities it
reaches 8% or more.

The chloride occurs to the extent of 0-5 -2'5% in ammonia soda or 0'25--o*5%
in Leblanc soda,

Pure or chemically pure- sodium Mtrhonaic. should answer all the qualitative
tests, i-:t'4.


NaflCK, -  106-5

White, crystals or powder soluble in about i part of cold water. The
commercial product does not reach the degree of purity of potassium
chlorate, but usually contains small quantities of chlorides, lime and, some-
times, iron. The various impurities and also the content of chlorate are
investigated and determined as in potassium chlorate (</.,) : i c.c. N/io-
thiosulphatc 0-001775 gram NaC103.knowing that I c.c. of silver solution = 1-3 c.c. N/io-iodine.